Slow irregular variable

A slow irregular variable (ascribed the GCVS types L, LB and LC) is a variable star that exhibit no or very poorly defined periodicity in their slowly changing light emissions. These stars have often been little-studied, and once more is learnt about them, they are reclassified into other categories such as semiregular variables.

Nomenclature

Irregular variable stars were first given acronyms based on the letter "I": Ia, Ib. and Ic.[1] These were later refined so that the I codes were used "nebular" or "rapidly irregular" variable stars such as T Tauri and Orion variables. The remaining irregular stars, cool slowly varying giants and supergiants of type Ib or Ic were reassigned to Lb and Lc.[2] When the General Catalogue of Variable Stars standardised its acronyms to be all uppercase, the codes LB and LC were used.[3]

Type Lb

Slow irregular variables of late spectral types (K, M, C, S); as a rule, they are giants[3]

The GCVS also claims to give this type to slow irregular red variables where the luminosity or spectral type is not known, although it also uses the type L for slow irregular red stars where the spectral type or luminosity is unclear. The K5 star CO Cygni is given as a representative example.[3]

Type Lc

Irregular variable supergiants of late spectral types having amplitudes of about 1 mag in V[3]

The M2 supergiant TZ Cassiopeiae is given as a representative example.[3]

List

List of Slow Irregular Variables[4]
Designation (name) Constellation Discovery Apparent magnitude (Maximum)[5] Apparent magnitude (Minimum)[5] Range of magnitude Spectral type Subtype Comment
U Antliae Antlia   8m.1 (p) 9m.7 (p) 1.6 N:v Lb  
Beta Pegasi Pegasus Schmidt, 1847 2m.31 2m.74 0.43 M2.3 II-III Lb  
Epsilon Pegasi (Enif) Pegasus 0m.7 3m.5 2.8 K2 Ib Lc  
TX Piscium Pisces   4m.79 5m.20 0.42 C5 III Lb  
Alpha Scorpii (Antares) Scorpius   0m.88 1m.16 0.28 M1.5 Iab-b Lc  
Alpha Tauri (Aldebaran) Taurus   0m.75 0m.95 0.20 K5 III Lb  
Mu Geminorum Gemini   2m.75 3m.02 0.28 M3 III Lb  
BE Camelopardalis Camelopardalis   4m.35 4m.48 0.13 M2 II Lc  
Tau4 Eridani Eridanus   3m.57 3m.72 0.15 M3 III Lb  
13 Boötis Bootes   5m.29 5m.38 0.09 M2 IIIab Lb  
Psi Virginis Virgo   4m.73 4m.96 0.23 M3 III Lb  
V854 Arae Ara   5m.84 5m.99 0.12 M1.5 III Lb  
62 Sagittarii Sagittarius   4m.45 4m.62 0.17 M4 III Lb  
TX Piscium Pisces   4m.79 5m.20 0.41 C5 III Lb  
CQ Camelopardalis Camelopardalis   5m.15 5m.27 0.12 M0 II Lc  
Pi Aurigae Auriga   4m.24 4m.34 0.10 M3.5 II Lc  
NO Aurigae Auriga   6m.06 6m.44 0.58 M2 Iab Lc  
Omicron1 Canis Majoris Canis Major   3m.78 3m.99 0.21 M2.5 Iab Lc  
Sigma Canis Majoris Canis Major   3m.43 3m.51 0.08 M1.5 Iab Lc  
NS Puppis Puppis   4m.4 4m.5 0.1 K3 Ib Lc  
Lambda Velorum Vela   2m.14 2m.30 0.16 K4 Ib-IIa Lc  
V337 Carinae Carina   3m.36 3m.44 0.08 K3 II Lc  
GZ Velorum Vela   3m.43 3m.81 0.38 K3 II Lc  
RX Telescopii Telescopium   6m.6 7m.4 0.8 M3 Iab Lc  

Other irregular variables

There are a number of other types of variable stars lacking clearly detectable periods, and which are sometimes referred to as irregular variables:[4]

In addition, many types of eruptive or cataclysmic variable are highly unpredictable.[4]

References

  1. ^ Kholopov, P. N. (1959). "A Revised List of T-Associations and Their Members". Soviet Astronomy. 3: 291. Bibcode:1959SvA.....3..291K.
  2. ^ Mayall, Margaret W. (1964). "Variable Star Notes- from the XII General Assembly, I.A.U.; 043274 X Camelopardalis". Journal of the Royal Astronomical Society of Canada. 58: 283. Bibcode:1964JRASC..58..283M.
  3. ^ a b c d e "GCVS Variability Types". Retrieved 2016-09-04.
  4. ^ a b c Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S. 1: 02025. Bibcode:2009yCat....102025S.
  5. ^ a b (visual magnitude, unless marked (B) (= blue) or (p) (= photographic))

External links

1 Lyncis

1 Lyncis is a single star in the northern constellation of Lynx. It is also known by its variable star designation of UW Lyncis; 1 Lyncis is the Flamsteed designation. This object is visible to the naked eye as a faint, reddish-hued star with an apparent visual magnitude of 4.95. It is moving further from the Earth with a heliocentric radial velocity of 12 km/s.The star is an aging red giant of spectral type M3IIIab, currently on the asymptotic giant branch, having exhausted the hydrogen at its core and evolved away from the main sequence. It has been classified as a slow irregular variable, after being found to be slightly variable in 1969 by Olin J. Eggen. Its changes in brightness are complex, with two shorter changeable periods of 35–40 and 47–50 days due to the star's pulsations, and a longer period of 1500 days possibly due to the star's rotation or convectively induced oscillatory thermal (COT) mode. The star has expanded to 156 times the Sun's radius and it is radiating 2,848 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 3,485 K.

3 Aquarii

3 Aquarii (abbreviated 3 Aqr) is a variable star in the equatorial constellation of Aquarius. 3 Aquarii is the Flamsteed designation; it also bears the Bayer designation k Aquarii and the variable star designation EN Aquarii. With a mean apparent visual magnitude of 4.429, it is visible to the naked eye in dark skies. It has an annual parallax shift of 5.57 milliarcseconds with a 5% margin of error, which translates to a physical distance of around 590 light-years (180 parsecs) from Earth.

With a stellar classification of M3 III, this is a red giant star that has exhausted the hydrogen at its core and evolved away from the main sequence of stars like the Sun. It is classified as a slow irregular variable, type Lb, and the luminosity of this star varies over time, following multiple periods of variability. The measured angular diameter of this star, after correction for limb darkening, is 5.60 ± 0.70 mas. At the estimated distance of 3 Aquarii, this yields a physical size of about 108 times the radius of the Sun. The effective temperature of the outer atmosphere is 3,933 K, giving this star the cool reddish hue of an M-type star.

47 Cygni

47 Cygni is a triple star system in the northern constellation of Cygnus, and is located around 4,000 light years from the Earth. It is visible to the naked eye with a combined apparent visual magnitude of 4.61. The system is moving closer to the Earth with a heliocentric radial velocity of −4.6 km/s.The dual nature of this system was recognized by Annie Cannon in 1912, and she assigned the pair separate Henry Draper Catalogue identifiers. They orbit each other with a period of around 143.69 yr. The primary component is itself a spectroscopic binary in a near circular orbit with a period of around 3.06 yr. The a sin i value for the primary is 30.8 ± 1.6 Gm (0.206 ± 0.011 AU), where a is the semimajor axis and i is the orbital inclination. It has been repeatedly resolved by speckle interferometery since 1973. Radio emission was detected from this system in 1985/86.The supergiant primary is a slow irregular variable with an amplitude of about 0.1 magnitudes. Its close companion has 57% of the mass of the Sun. The secondary is a hot B-type main-sequence star, but still 2.5 magnitudes fainter than the primary.

5 Lacertae

5 Lacertae (5 Lac) is a spectroscopic binary in the constellation Lacerta. Its apparent magnitude is 4.36.

5 Lacertae is a slow irregular variable star with a small amplitude. Photometry from the Hipparcos satellite showed brightness changes between Hipparcos magnitudes 4.39 and 4.56 with no clear periodicity. It was given the variable star designation V412 Lacertae in 1999 in a special name-list dedicated to variables detected from Hipparcos.The spectrum of 5 Lacertae clearly indicates both a hot component and a cooler component, recognised even in early spectra. Published spectral types for the brighter cool component vary from K4 to M0, with a luminosity class of giant or supergiant. The hotter star is generally classed as a relatively unevolved late B or early A star, but an automated classification program gave it a spectral class of B2V.Radial velocity variations in the absorption lines from the two separate stars have been measured to determine the orbit. This has an unusually long period of almost 42 years. The two stars have an eccentric orbit with a projected axis of about 15 au.

7 Ceti

7 Ceti is a single, variable star in the equatorial constellation of Cetus. It has the variable star designation AE Ceti. The star is visible to the naked eye with a baseline apparent visual magnitude of 4.44. Based upon an annual parallax shift of only 7.3 mas, it is located roughly 450 light years away. It is moving closer to the Sun with a heliocentric radial velocity of −23 km/s. Eggen (1965) listed it as a probable member of the Wolf 630 group of co-moving stars.This is an aging red giant star with a stellar classification of M1 III, currently on the asymptotic giant branch. Samus et al. (2017) has it classed as a slow irregular variable of type LB:, and ranges in magnitude from 4.26 down to 4.46. Tabur et al. (2009) list it as a semiregular variable with four known periods ranging in frequency from 19.2 to 41.7 days. The stellar atmosphere of 7 Ceti has expanded to an estimated 54 times the Sun's radius. It is radiating around 1,019 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,800 K.

AW Canum Venaticorum

AW Canum Venaticorum is a variable star in the constellation Canes Venatici. It is visible to the naked eye with a nominal apparent visual magnitude of 4.76. The distance to this star, as measured from its annual parallax shift of 5.3 mas, is around 620 light years. It is moving closer with a heliocentric radial velocity of −44 km/s.At the age of 1.1 billion years, this is an evolved red giant star with a stellar classification of M3- IIIa. It is a slow irregular variable of type Lb, with a brightness that ranges between magnitudes 4.73 and 4.85. The star has 2.2 times the mass of the Sun and has expanded to 117 times the Sun's radius. It is radiating 2,387 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,529 K.

BI Cygni

BI Cygni (BI Cyg, IRC +40408, BD+36 4025) is a red supergiant in the constellation Cygnus. It is an irregular variable star with a maximum brightness of magnitude 8.4 and a minimum of magnitude 9.9. It has a current mass of 20 M☉.It is considered a member of the stellar Cygnus OB1 association, its distance is 1,580 parsecs (5,150 light-years) of the Solar System. It is less than a degree south of another variable red supergiant, BC Cygni.

BI Cyg is a slow irregular variable star classified as type Lc, an irregular supergiant. Its brightness changes between extremes of magnitude 8.4 and 9.9. Frequency analysis of its light curve shows no significant periods.BI Cyg is one of the largest known stars with a radius around 1,240 R☉ based on the assumption of an effective temperature of 3,575 K and a bolometric luminosity of 226,000 L☉. More recent studies derive lower luminosities below 130,000 L☉, suggesting an initial mass of 20 M☉, and consequently lower values for the radius.

BQ Octantis

BQ Octantis (BQ Oct) is a slow irregular variable star in the constellation Octans. It is a red giant with an apparent magnitude of 6.82.

DU Crucis

DU Crucis is a red supergiant and slow irregular variable star in the open cluster NGC 4755, which is also known as the Kappa (κ) Crucis Cluster or Jewel Box Cluster.

GZ Velorum

GZ Velorum is a single, orange-hued star in the southern constellation of Vela. It is a faint star but visible to the naked eye, having an apparent visual magnitude of 4.58. The star is located around 1,300 light years from Earth, as determined from its annual parallax shift of 2.4 mas. It is moving further away with a heliocentric radial velocity of +13 km/s.This is a bright giant star with a stellar classification of K2.5 II. It is a slow irregular variable of type LC with a frequency of 0.16585 cycles per day. In the R (red) band, the magnitude of the star ranges from 3.43 down to 3.81. The measured angular diameter of this star, after correction for limb darkening, is 3.17±0.04 mas. At the estimated distance of GZ Vel, this yields a physical size of about 140 times the radius of the Sun.GZ Vel is 30 million years old with 9 times the mass of the Sun. It is radiating 9,241 times the Sun's luminosity from its photosphere at an effective temperature of 4,140 K.

Gamma Phoenicis

Gamma Phoenicis is a star system in the constellation Phoenix, located around 71.63 parsecs (233.6 ly) distant.γ Phoenicis is a spectroscopic binary and a small amplitude variable star. The star system shows regular variations in brightness that were reported as a 97.5 day period in the Hipparcos catalogue, but have since been ascribed to a 193-day orbital period with primary and secondary minima. Although the light curve appears to show eclipses, the high orbital inclination suggests the variations are due to ellipsoidal stars as they rotate in their orbit. γ Phoenicis is listed in the General Catalogue of Variable Stars as a possible slow irregular variable with a range from 3.39 to 3.49, the same as reported for the eclipses or ellipsoidal variations.Only the primary star in the γ Phoenicis system is visible. The second is inferred solely from variations in the radial velocity of the primary star. The primary is a red giant of spectral type M0III, a star that has used up its core hydrogen, then expanded and cooled as it burns a shell of hydrogen around an inert helium core. The two stars are estimated to have masses of 1.3 M☉ and 0.6 M☉ respectively. The primary is over five hundred times more luminous than the sun. The system shows signs of hot coronal activity, although the primary star is too cool for this. It may originate on the secondary, possibly as material is accreted from the cool giant primary.

IZ Aquarii

IZ Aquarii is a red giant star in the constellation Aquarius. It is a slow irregular variable that varies between magnitudes 6.23 and 6.47.

Mu1 Cancri

Mu1 Cancri, Latinized from μ1 Cancri, is a evolved red giant star in the zodiac constellation of Cancer. Parallax measurements made by the Hipparcos spacecraft put it about 740 light years (230 parsecs) from the Sun. At that distance, the visual magnitude is diminished by an extinction factor of 0.28. The name Mu1 comes from the Bayer naming system: the "1" in the name is because (from Earth) it appears to be close to 10 Cancri (Mu2 Cancri). Mu1 Cancri is a variable star and was given the variable star designation BL Cancri. It is a slow irregular variable with periods of 22.6, 37.8, and 203.7 days.

Nu Tucanae

Nu Tucanae (ν Tuc, ν Tucanae) is a solitary star in the southern constellation of Tucana.

Nu Tucanae is a M-type red giant with a mean apparent magnitude of +4.91. It is approximately 290 light years from Earth. It is classified as a slow irregular variable and its brightness varies from magnitude +4.75 to +4.93. Periods of 22.3, 24.4, 24.8, 25.1, 25.5, 33.8, 50.6, 80.1, 123.2, and 261.8 days have been reported.

Pi Aurigae

Pi Aurigae, Latinized from π Aurigae, is the Bayer designation for a single, red-hued star in the northern constellation of Auriga. Located about one degree north of the 2nd magnitude star Beta Aurigae, Pi Aurigae is visible to the naked eye with an apparent visual magnitude of 4.25 Based upon parallax measurements, it is approximately 800 light-years (250 parsecs) away from Earth. At that distance, the brightness of the star is diminished by 0.54 in magnitude from extinction caused by interstellar gas and dust.Pi Aurigae is an evolved bright giant star with a stellar classification of M3 II. The measured angular diameter of this star, after correction for limb darkening, is 9.56 ± 0.10 mas. At the estimated distance of Pi Aurigae, this yields a physical size of about 265 times the radius of the Sun. On average, the star is radiating 6,493 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,388 K. It is classified as a slow irregular variable of type LC and its brightness varies from magnitude +4.24 to +4.34.

Psi1 Aurigae

Psi1 Aurigae (ψ1 Aur, ψ1 Aurigae) is a star in the northern constellation of Auriga. It is faintly visible to the naked eye with an apparent visual magnitude of 4.91. Based upon a measured annual parallax shift of 0.82 mas, it is approximately 4,000 light-years (1,200 parsecs) distant from the Earth.

This is a massive supergiant star with a stellar classification of M0 I. It is a slow irregular variable of the LC type, with its brightness varying in magnitude by 0.44. The star is more than 14 times as massive as the Sun and is blazing with 63,579 times the Sun's luminosity. This energy is being radiated into outer space from its outer atmosphere at an effective temperature of 3,750 K, giving it the orange-red hue of a cool M-type star.

TZ Cassiopeiae

TZ Cassiopeaie (TZ Cas, HIP 117763, SAO 20912) is a variable star in the constellation Cassiopeia with an apparent magnitude of around +9 to +10. It is approximately 8,000 light-years away from Earth. The star is a red supergiant star with a spectral type of M3 and a temperature below 4000 Kelvin.

TZ Cassiopeiae was reported as being variable by Williamina Fleming and published posthumously in 1911. It is a slow irregular variable star with a possible period of 3,100 days. It is over 60,000 times the luminosity of the Sun, and it is 645 to 800 times larger than the Sun. It is a member of the Cas OB5 stellar association, together with the nearby red supergiant PZ Cassiopeiae.The initial mass of TZ Cassiopeiae has been estimated from its position relative to theoretical stellar evolutionary tracks to be around 15 M☉.TZ Cas is losing mass through a powerful stellar wind at two millionths of a solar mass each year. It is unclear whether this is sufficient to cause the star to lose its atmosphere and become a blue supergiant before the core exhausts its fuel and collapses as a supernova. Either as a red or blue supergiant, or a Wolf-Rayet star, it will inevitably end its life violently in a supernova explosion when the core collapse occurs.

V385 Andromedae

V385 Andromedae is a variable star in the constellation Andromeda, about 360 parsecs (1,200 ly) away. It is a red giant over a hundred times larger than the sun. It has an apparent magnitude around 6.4, just about visible to the naked eye in ideal conditions.

V385 Andromedae was identified as a long-period variable in 1999 from analysis of Hipparcos photometry. It was classified as a slow irregular variable, but analysis of its light curve identified a possible 36 day period. It varies by about 0.1 magnitudes.

V528 Carinae

V528 Carinae (V528 Car, HD 95950, HIP 54021) is a variable star in the constellation Carina.

V528 Carinae has an apparent visual magnitude of +6.75. It is a distant star but the exact distance is uncertain. The Hipparcos satellite gives a negative annual parallax and is not helpful. Its Carina OB2 membership allows the distance to be estimated at 3,850 light-years.V528 Carinae is a red supergiant of spectral type M2 Ib with an effective temperature of 3,700 K. It has a radius of 700 solar radii, making it one of the largest stars. In the visible spectrum luminosity is 11,900 times higher than the sun, but the bolometric luminosity considering all wavelengths reaches 81,000 L☉. It loses mass at 0.5×10−9 M☉ per year.It is classified as a slow irregular variable whose prototype is TZ Cassiopeiae.

Pulsating
Eruptive
Cataclysmic
Rotating
Eclipsing

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